1. Field of the Invention
The present invention relates to an image forming apparatus, such as a laser beam printer, which employs a light deflector having a microstructure, and also relates to a control method for the image forming apparatus.
2. Description of the Related Art
Hitherto, a rotatable multi-faceted mirror, e.g., a polygonal mirror, has been used as a light (beam) deflector in an image forming apparatus. As a technique to be substituted for the polygonal mirror, a light deflector has been recently proposed in which a mirror is driven at a resonance frequency to deflect a light beam. In comparison with a light scanning optical system which uses the rotatable multi-faceted mirror such as the polygonal mirror, the resonance-type light deflector is advantageous in that, for example, the deflector size can be greatly reduced and power consumption is small. Another advantageous feature of the resonance-type light deflector is that no face tangle exists theoretically. In particular, when a light deflector is manufactured using a single-crystal Si through a semiconductor process, the light deflector is theoretically free from metal fatigue and has superior durability.
Typically, the resonance-type light deflector includes a moving element, a torsion spring, and a support for supporting those elements. The resonance frequency of that light deflector is determined based on the inertial moment of the moving element and the spring constant of the torsion spring. Further, because the spring constant of the torsion spring depends on temperature, the resonance frequency of the light deflector is changed depending on the environmental temperature. Accordingly, when the resonance frequency of the light deflector is shifted as a result of temperature change, the frequency of a driving signal is required to be adjusted.
Japanese Patent Laid-Open No. 2005-292627 discloses a technique of detecting the oscillating position of a mirror in a light deflector and adjusting a driving signal for the light deflector based on the detected position information. More specifically, a light beam generated from a light beam generation unit is deflected for scanning by a deflecting mirror (light deflector) which can be driven by the driving signal, and a light sensor detects the timing at which the light beam passes a predetermined position. With the technique disclosed in Japanese Patent Laid-Open No. 2005-292627, the driving signal is adjusted based on the timing at which the light beam is received by the light sensor.
In the case using the above-described light deflector in an image forming apparatus, however, if the driving signal is adjusted during image formation, the driving signal for the light deflector is changed during printing, thus causing deterioration of printing accuracy.
A light beam generation unit and a photosensitive member can be controlled in conjunction with the operation of the light deflector so that the printing accuracy is not deteriorated even when the driving signal is adjusted during image formation. However, such a solution requires complicated control of the light deflector, the light beam, and the photosensitive member.